Refrigerating equipment for cooling a fluid

ABSTRACT

The invention relates to refrigerating apparatus for cooling a fluid which may be either a liquid or a gas. The components include, in addition to the conventional compressor, condenser and evaporator, a pilot evaporator unit on the downstream side of the evaporator. The fluid to be cooled is passed through the drier prior to being passed through the evaporator. This has the main effect of increasing the effective capacity of the main evaporator by facilitating an optimum regulating operation.

United States Patent Huelle [4 1 Aug. 1, 1972 [54] REFRIGERATING EQUIPMENT FOR [56] References Cited COOLING A FLUID UNITED STATES PATENTS 72 I entor: Zb' R. H l 1 f 'm 2,052,410 8/1936 Kucher ..62/503 [73] Assignee: Danfoss A/S, Nordborg, Denmark primary Examiner Meyer P fli 22 Filed: March 18, 1970 yy Easwn F A The invention relates to refrigerating apparatus for omgn pphcauon Pnomy Data cooling a fluid which may be either a liquid or a gas.

April 16, 1969 Germany 19 19 231-5 The components include, in addition to the conventional compressor, condenser and evaporator, a pilot [52] U.S. Cl. ..62/225, 62/389, 62/503, evaporator unit on the downstream i f the Int Cl F2 52 evaporator. The fluid to be cooled is passed through I a n I s s e a t e n [58] Field of Search This has the main effect of increasing the effective capacity of the main evaporator by facilitating an optimum regulating operation.

3 Claims, 3 Drawing Figures ii i :F' I i 5 REFRIGERATING EQUIPMENT FOR COOLING A FLUID The invention relates to refrigerating equipment comprising an evaporator for cooling a fluid, a heatable pilot evaporator and a valve for regulating the feed of the fluid refrigerating medium into the main evaporator, in dependence upon the excess heat of the refrigerating medium at the end of the drier.

Refrigerating equipment is often regulated with the help of a thermostatic expansion valve, which is controlled by the excess heating of the refrigerating medium upon its emergence from the evaporator. By the term excess heating is meant the difference between the temperature of evaporation of the refrigerating medium and the temperature of the emerging refrigerating medium.

In order to utilize the evaporator in an optimum manner, efforts are made to fill it as completely as possible with evaporating refrigerating medium. lf filling is incomplete, only part of the heat exchange surface of the evaporator is fully effective. On the other hand, it is not possible to fill the evaporator 100 percent, since otherwise the excess heating of the refrigerating medium becomes so small that it no longer constitutes a signal that can be used for actuating the valve. Furthermore, despite operating conditions remaining constant, virtually uncontrollable fluctuations in the point at which evaporation ends occur in the tubular evaporator, so that if the evaporator is completely filled with evaporating refrigerating medium, fluid refrigerating medium emerges intermittently from the evaporator, so that the excess heating drops to zero, and damage may also be caused in the compressor connected beyond the evaporator. Because of these difficulties, it has been necessary to adjust the thermostatic expansion valve so that, at nominal capacity, a not inconsiderable portion of the evaporator is freed from evaporating refrigerating medium.

To overcome this drawback, a pilot evaporator unit has been fitted beyond the evaporator, this unit being heated by fluid refrigerating medium. By using an appropriate size of pilot evaporator unit it was possible to ensure that, even with the main evaporator completely filled with evaporating refrigerating medium, no fluid refrigerating medium was able to pass into the suction pipe and to the compressor and that, beyond the pilot evaporator unit, excess heating of such magnitude could be obtained that a clear signal for the thermostatic expansion valve was obtained. Surprisingly considerable difficulties in regulation were observed however; in particular it was practically impossible so to adjust the thermostatic expansion valve that the main evaporator was substantially completely filled for a prescribed capacity range.

The object of the invention is to provide refrigerating equipment which, while being of simpleconstruction, enables the heat exchange surface of the evaporator to be utilized as completely as possible, and which in addition has good regulating and, in particular, adjustment characteristics.

To achieve this object, refrigerating equipment of the initially described kind is characterized in that the pilot evaporator unit can be heated by the refrigerating medium.

In prior art equipment, no account was taken of the fact that the fluid refrigerating medium has a very constant temperature. If the completely filled evaporator is operated-at very low capacity, the refrigerating medium flows slowly through the pilot evaporator unit and undergoes considerable excess heating. If, however, the completely filled evaporator is operated at higher capacity, the refrigerating medium flows more rapidly through the pilot evaporator unit and undergoes less excess heating. In the first case, the thermostatic expansion valve, acting as a proportional regulator, there'- fore opens more widely than in the second case. This however, is just the opposite of what is required as regards regulating characteristics, since the valve must open more widely at higher capacity than at lower capacity.

If, on the other hand, the pilot evaporator unit is heated by the medium to be cooled, not only is the required complete evaporation of the fluid refrigerating medium emerging from the evaporator achieved, but, in addition, the excess heating is correctly altered in dependence upon capacity, since the capacity provided by the main evaporator depends to a very great extent upon the temperature of the medium to be cooled. The higher the temperature, the greater is the capacity provided but, also, the greater is the excess heating reached in the drier, i.e., the greater is the cross-section of the opening of the expansion valve. At lower temperature, i.e. lower capacity, the overheating is also less and therefore so is the width to which the valve opens. By appropriate choice of size of the pilot evaporator unit the excess heating can be so selected that, in the prescribed working range of the refrigerating equipment or in the range over which the expansion valve can be adjusted, it provides values that can be used for controlling the valve.

It is particularly advantageous if the drier can be heated by the incoming medium to be cooled, since the considerations set forth apply in particular when considering the inlet temperature of the medium to be cooled. This temperature passes through a very great range in dependence upon the required capacity. Furthermore, it is at a relatively high value, i.e., a value favoring the excess heating of the outgoing refrigerating medium.

In the preferred case, the medium to be colled is a' liquid, in particular, water. The medium can however also be a salt solution, In the case of such liquids, extremely small driers can be used, which generally are of smaller size than the known driers heated by means of the condensate. Furthermore, the use of the principle of the invention in cooling such liquids offers particular advantage since the evaporators are normally of very small length with very large heat-exchange surfaces.

In this connection it is advantageous that the ratio of the length of the pilot evaporator unit to its heatexchange surface be a multiple of that of the main evaporator. The length of the drier can then be so selected that entrained liquid particles are in any case still evaporated; the heat exchange is then still sufficient in any case when heating is carried out by the medium to be cooled. This requirement is met for example in the case of an evaporator having several evaporator tubes arranged in parallel, and a pilot unit comprising just a single tube.

In a practical arrangement, the pilot can be fonned for example by passing a pipe for the refrigerating medium emerging from the main evaporator through a.

portion of thetube for the incoming medium to be cooled. A simple arrangement of this kind is often possible, since the cross-section of the pipe for the medium to be cooled is as a rule greater than the crosssection of the suction pipe leading to the compressor. For example, the diameter of the refrigerating medium pipe is 1.5 inch, whereas the diameter of the suction pipe is only 0.75 inch.

A further possible arrangement is that wherein the pilot unit is formed by passing a pipe forthe refrigerating medium emerging from the main evaporator back through the evaporator chamber accommodating the medium to be cooled. By passing this tube through the main evaporator chamber over a straight line, there is obtained a drying path of a length equal to that of the main evaporator, which length, at least partially, is directly acted upon by the incoming medium to be cooled. I

A further improvement can be achieved by, as in an earlier proposal, providing the passage carrying the outgoing refrigerating medium in the pilot unit with means on its inner wall for reinforcing the wetting action by the fluid refrigerating medium, which means however leave the greater part of the cross-section of the passage unoccupied. These means can be constituted by, for example, an inserted wire mesh. Due to the capillary action, fluid refrigerating medium is preferentially held on the wall of the passage and is consequently evaporated more rapidly.

The invention will now be described in more detail by reference to embodiments illustrated schematically in the drawing, in which: 1

FIG. 1 is a diagram of the refrigerating equipment of the invention,

FIG. 2 shows a specific form of main evaporator and pilot evaporator unit, and

FIG. 3 shows a further form of evaporator and drier.

In cooling equipment as shown in FIG. 1, a refrigerating medium compressor 1, a condenser 2, a thermostatic expansion valve 3, a main evaporator 4 and a pilot evaporator unit 5 are arranged one after the other in the refrigerating circuit. The medium to be cooled, here water, is introduced through a pipe 6 into the pilot unit 5, is passed through a connecting pipe 7 to the main evaporator 4, and thence is passed through a pipe 8 to the consumer unit. The valve 3 has a working element 9, which by way of a first impulse line 10, is acted upon by the pressure of the refrigerating medium behind the valve 3, and, by way of a second impulse line 11, by the temperature behind the pilot unit 5, which temperature is picked up by a sensor 12. The pressure in the line, 10 is at the same time a measure of the evaporation temperature of the refrigerating mediurn, so that the excess heating of the refrigerating medium acts as a setting factor in the working element 9, by differentiation.

The higher the temperature of the incoming water in the pipe 6, the higher is the refrigerating capacity provided by the refrigerating equipment. Higher initial temperature of the water leads to a more pronounced excess heating in the pilot unit 5. The sensor 12 sends a more powerful signal and the valve 3 sets itself to a greater cross-section of opening, so that a greater quantity of refrigerating medium per unit of time passes into the main evaporator 4 and is there available for producing this refrigerating capacity.

When tuning up this refrigerating equipment, the thermostatic expansion valve 3 can be so set that the main evaporator 4 is substantially completely filled for a prescribed capacity. If, in the same equipment, a different capacity is required, the valve 3 sets itself automatically without any difficulties arising as regards regulation.

FIG. 2 shows a specific form of the pilot unit of the invention. The same reference numerals as in FIG. 1 are used for like parts. The pipe 13 for the refrigerating medium, extending from the main evaporator 4, is passed by way of a section 14 through the supply pipe 6 for the incoming water. The required heating is achieved in this section 14.

A cylindrical wire mesh is inserted in the tube 13 in the area of the section 14, which wire mesh retains liquid refrigerating medium to an increased extent by capillary action and enables it to evaporate more readily.

Whereas FIG. 1 illustrates a thermostatic expansion valve having the so-called internal compensation, and the line 10 is formed by an inner connection in the valve casing, FIG. 2 shows a thermostatic expansion valve having the so-called external compensation, the line 10 not being connected directly behind the valve but behind the main evaporator so as to eliminate the effect of the main pressure-drop in the evaporator. The line 10 enters the suction pipe behind the sensor 12 in the direction of flow. This ensures that no traces of refrigerating medium, passing through the signal line 10' into the section pipe, can interfere with the signal at the sensor 12.

Finally, FIG. 3 illustrates, in the case of a main evaporator 4 having a plurality of evaporator pipes arranged in parallel, how the outlet pipe 16 is simply passed back through the chamber of the evaporator 4, accommodating the cooling medium, a pilot evaporator unit 17 being thus formed. The initial portion of this unit is located near the inlet pipe 6 for the medium to be cooled, so that the advantage of utilizing the inlet temperature of this medium to be cooled is also achieved.

lclaim:

1. Refrigerating equipment for cooling a fluid comprising, a compressor, a condenser, a main evaporator, a valve between said condenser and said evaporator for regulating the flow of refrigerant to said evaporator, a separate pilot evaporator unit, refrigerant conduit means having a first portion thereof in said main evaporator and a second portion thereof in said pilot evaporator unit, fluid conduit means having an upstream portion thereof in said pilot evaporator unit and downstream portion thereof in said main evaporator, and temperature sensing means on the downstream side of said second portion refrigerant conduit means for controlling said valve.

2. Refrigeration equipment according to claim 1 wherein said fluid to be cooled is a liquid.

3. Refrigeration equipment according to claim 1 wherein the ratio of the length of said pilot evaporator to the area of its heat exchange surface is a multiple of the length of said evaporator to the area of its heat exchange surface. 

1. Refrigerating equipment for cooling a fluid comprising, a compressor, a condenser, a main evaporator, a valve between said condenser and said evaporator for regulating the flow of refrigerant to said evaporator, a separate pilot evaporator unit, refrigerant conduit means having a first portion thereof in said main evaporator and a second portion thereof in said pilot evaporator unit, fluid conduit means having an upstream portion thereof in said pilot evaporator unit and downstream portion thereof in said main evaporator, and temperature sensing means on the downstream side of said second portion refrigerant conduit means for controlling said valve.
 2. Refrigeration equipment according to claim 1 wherein said fluid to be cooled is a liquid.
 3. Refrigeration equipment according to claim 1 wherein the ratio of the length of said pilot evaporator to the area of its heat exchange surface is a multiple of the length of said evaporator to the area of its heat exchange surface. 